8.3 Coral reefs

Question 1

What is the importance of coral reefs?

Answer 1

• Seafood: yield up to 15 tons of fish/other seafood per km squared
• estimated can provide food for up to a billion people in Asia alone
• Tourism: snorkelling/scuba diving is especially popular in the Red Sea
• much needed income in LICs
• Medical products: in rainforest some of the organisms living in the reef produce chemicals that can be used to cure disease, potentially including skin cancer and some viral diseases
• Coastal protection: coral reefs protect coastline from storm waves and can even break the power of tsunami waves
• especially important in areas where storms likely
• jewellery

Question 2

What are the different types of coral reefs?

Answer 2

fringing reefs: grow near coastline around island/continents. Most common type.

barrier reefs: parallel to coastline, but separated by deep wide lagoons. At their shallowest points, they can reach water’s surface forming a “barrier” to navigation

atolls: rings of coral that create protected lagoons and are usually located in middle of the sea. Usually form when islands surrounded by fringing reefs sink into the sea/sea levels rises around them.

Question 3

What are the conditions needed for coral growth?

Answer 3

Light:
- cannot grow in the water deeper than 30m as need sunlight to photosynthesise
- corals feed on plankton, need sunlight

Wave action:
- sufficient wave action which oxygenates the water so that the coral polyps can respire
- but too strong wave action can damage the structure of the calcium carbonate skeletons and risk erosion occurring increasing sediment levels

Salinity:
- grow best where salt levels are high
- prefer seawater with salinity levels between 32 and 42 psu

Sea bed:
- has to be solid surface which reef can grow on
- so form in shallow offshore waters

Sediment:
- polyps need Clean, clear, sunlit water so can’t live where rivers bring muddy sediments into sea and also need sediment clogs up feeding systems of coral polyps

Exposure to air:
- can’t survive for long above the water, so most of the reef is at or below low tide level

Temperature:
- must be above 18 degrees
- grow best where sea surface temp between 23 and 25 degrees why most are found between 30 degrees north and south of the equator
-

Question 4

What is the characteristics of an Atoll?

Answer 4

• Shape: ring-shaped coral reef enclosing a lagoon
• Lagoon: central lagoon, often relatively shallow
• Biodiversity: high biodiversity, with a variety of coral species, fish and other marine life

Question 5

How do Atolls form?

Answer 5

• atolls consist of a ring shaped piece of coral situated away from the shore with a deep central lagoon
  1. Volcanic island forms and a reef starts to grow around the island parallel to the coastline, forming a fringing reef
  2. Island then begins to subside; it sinks due to rising sea levels or plate tectonics
  3. This forms a central lagoon up to 50 meters deep and the reef separates fro the island forming a barrier reef
  4. Complete submergence of the island then occurs but the coral reef continues to grow upwards as it has increased input available and the central lagoon becomes deeper - atoll

Question 6

What is the distribution of atolls?

Answer 6

Geographic distribution: found in pacific/indian oceans
Pacific ocean: e.g Caroline, Marshall and Tuamotu archipelagos
Indian Ocean: Maldives

Question 7

What are the characteristics of Fringing Reefs?

Answer 7

Proximity to shore: directly attached to the shore with no significant lagoon between reef/land
- Slope: gentle slope on shoreward side and steeper slope on seaward side
- Biodiversity: diverse
- Water depth: shallow water

Question 8

How do fringing reefs form?

Answer 8

1. Coral polyp settlement: coral larvae settle on submerged rocks/hard surfaces in shallow waters
2. Growth and colonisation: these larvae develop into coral polyps, which beging to grow to form colonies. As they thrive, they secrete calcium carbonate, creating hard skeleton that contributes to the reef strucutr
3. Expansion: as more polyps settle and grow, reef expands outward from the shore

Question 9

What is the distribution of fringing reefs?

Answer 9

• Tropics: found where water temps suitable
• Caribbean: Bahamas
• Red sea: coastlines of Egypt
• Pacific oceans: coastline of Australia

Question 10

What are the characteristics of barrier reefs?

Answer 10

• distance from shore: separated from mainland by wide, deep lagoon
• Lagoon: several km wide and vary in depth
• size: larger/more continuous than fringing reefs, stretching hundreds of km
• biodiversity: high

Question 11

What is the formation of barrier reefs?

Answer 11

1. Initial fringing reef stage: start forming adjacent to the coast
2. subsidence and separation: as land/island subsides lagoon forms between the reef and the shore
3. reef growth: coral continues to grow upwards/outwards, maintaining its position near the surface as land subsides

Question 12

What is the distribution of barrier reefs?

Answer 12

• Great barrier Reef: Queensland, Australia
• Belize barrier Reef: coast of Caribbean sea
• New Caledonia Barrier Reef: southwest pacific ocean

Question 13

How does global warming threat coral reefs and impacts?

Answer 13

Threat:
- coral bleaching occurs when ocean temps too high for algae to survive in corals
- more diseases and invasive species may thrive in warmer waters potentially harming corals
- more frequent, strong storms can disrupt/destroy coral reefs
- higher levels of CO2 lead to acidification, decreases growth rate

Impacts:
Environmental:
- bleaching kills coral = loss of diversity/habitat
Social:
- loss of jobs due to decrease in tourism
- families may struggle who rely heavily on resources from ocean
- 50% drugs made for humans derived some way from nature
Economic:
- loss of tourist will occur if coral becomes unattractive = loss of GDP for gov who rely on it

Question 14

How does sea level rise threat coral reefs and what are its impacts?

Answer 14

Threat:
- increase in temperature = glaciers/ice sheets melting = rise in sea level
- if sea levels rise faster than upward growth of coral, may be too deep to receive sufficient sunlight
- rise in sea levels can cause increased coastal erosion, so more sediment is transported to the oceans, can lead to sedimentation in coral reefs, blocking sunlight
- especially in fringing reefs as close to shoreline

Question 15

How does El Nino threaten coral reefs ?

Answer 15

Threat:
- El Nino is a climate pattern that causes unusual warming of surface waters in the eastern Pacific Ocean
- may raise chances of coral bleaching across Great Barrier Reef
- during 2015-2016 even experienced prolonged periods of elevated sea temps

Question 16

How does acidification threaten coral reefs?

Answer 16

• significant increase in CO2 levels in the ocean
• when absorbed by seawater, triggers chemical reactions that result in increase in levels of H+ ions and decreases pH (more acidic)
• coral become bleach
• ocean’s pH dropped by about 0.1 units since start of industrial revolution

Impacts:
Environmental: coral cannot maintain calcium carbonate structures needed for growth/survival
- then leads to weaker coral skeletons = increased vulnerability to erosion
Social:
- fish begin to decline, health of relying locals does too
Economic:
- income/employment declines

Question 17

How is land based pollution a threat to coral reefs?

Answer 17

• chemicals in agricultural fertiliser = increased number of the Crown of Thorns starfish which warm oceans
• areas around ports have large amounts of shipping that also pollutes the sea, especially plastic waste which can smother/kill the coral
• raw sewage from tourism/coastal towns pollute seawater, cause water to be murky and block light affecting photosynthesis of algae
• even treated sewage and issue, contains phosphates from detergents which encourage growth of phytoplankton and crown of thorns starfish

Question 18

How is physical damage a threat to coral reefs?

Answer 18

• boating can physically disrupt coral reefs, e.g anchor dropped or large boats may bulldoze through and destroy coral
• destructive fishing practices can damage reefs: e.g bottom-trawling where large net dragged on sea floor

Question 19

How is tourism a threat to coral reefs?

Answer 19

• every year, 70 million trips to visit coral reefs for leisure
• tourism can form foundation for jobs, income and awareness, however tourists can also trample on the coral/disturb ecosystems

Impacts:
Environmental:
- breakage of coral colonies and tissue damage with direct contact such as walking and touching common when snorkelling
- water pollution by tour boats fuel discharge and human waste
- invasive species spread through fouling from recreational boating

Social/economic:
- less fish for locals to eat
- project 70% of reefs to vanish before 2030

Question 20

What are the main threats to Florida Keys coral reef? (case study)

Answer 20

• Local shops, such as Dive Key West shop, which sells scuba gear and runs boat charters rely on a healthy reef system, divers not interested in exploring dead/damaged reefs which do not attract as many fish and can be covered in algae
• Tourism is the economic engine of the Florida Keys – three and half million people visit each year and tourism supplies 54% of all island jobs and fuels a $2.7 billion economy**
• Less than 10% of the reef system is now covered with living coral
• reefs experienced back-to-back major bleaching events in 2014 and 2015
• Global warming main threat:
• Strong El Nino event of 1997-1998 which triggered widespread bleaching/coral death around the world
• 21 coral species in the Florida Reef Tract are suffering from multiple diseases and 7 of those are threatened under the Endangered Species Act
• Coral reefs worth $36 billion annually to tourism industries in key tropical coastal regions such as Florida/Hawaii

Question 21

What are the management strategies for florida keys coral reef (case study)?

Answer 21

• 20 feet under water at Pickles Reef, the Coral Restoration Foundation, based in Key Largo has implanted endangered staghorn corals across the reef
• The implants, are small but are growing steadily
• Federal program that certifies vessels that train their crews in proper coral protection practices, including following proper mooring rules/ensuring divers do not poke/prod the reefs

Question 22

Managing Coral reefs

Answer 22

• protected areas and exclusion zones
• preventing and controlling invasive species/predators: removing crown of thorns starfish
• limiting global warming/ocean acidification: greener energy sources
• education and awareness: sustainable driving practices

Question 23

great barrier reef importance

Answer 23

Biodiversity:
- 400 types of coral
- 1,500 species of fish, 4,000 species of mollusks
- over 215 bird species

Economic significance:
- tourism: over 2 million visitors annually, generating approximately AUD $6.4 billion and supporting 64,000 jobs

Question 24

Challenges to great barrier reef

Answer 24

1. coral bleaching: major bleaching events in 1998, 2002, 2016 and 2017
2. cyclones: Cyclone Yasi (2011), cause significant physical damage to coral structures.
3. Pollution/invasive species:
   - Increased outbreaks of crown-of-thorns starfish that feed on coral.

Question 25

management efforts in great barrier reef

Answer 25

1. Great Barrier Reef Marine Park Authority (GBRMPA):
   - established 1975: manages and regulates human activities in the reef area.
   - Implemented zoning plans
2. Reef Water Quality Plan:
   - Between 2009 and 2019, reductions in nitrogen runoff (28%) and sediment runoff (11%) were recorded.
   - Promotes sustainable farming practices:
   - Use of cover crops to prevent soil erosion.
   - Reduction of fertilizers and pesticides through precision farming techniques.
3. Crown-of-Thorns Starfish (COTS) Management:
   - Targeted removal campaigns using divers to manually cull starfish.
   - Deployment of robotic systems like the COTSbot, an underwater drone designed to locate and inject lethal doses of bile salts into starfish
   - 1.2 million starfish removed since start of program in 2012
4. Zoning Plan (2003):
   - Great Barrier Reef Marine Park Zoning Plan divides the reef into different zones with specific restrictions
   - 33% of the reef is protected from extractive activities, creating marine sanctuaries where ecosystems can recover